Rear discharge mower

ABSTRACT

A rear discharge mower comprising: a first shaft; a first blade that is rotated in unison with the first shaft; a second shaft that is configured to be rotated in a direction opposite from a rotational direction of the first shaft; a second blade that is rotated in unison with the second shaft, wherein a grass-clippings discharge path is formed through which grass clippings are discharged in a rearward direction from the area between the first shaft and second shaft; an enclosing casing that supports the blade shafts; and a power train that is accommodated in the enclosing casing and that transmits power to the first and second blade shafts.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of co-pending U.S. patentapplication Ser. No. 12/051,815 filed Mar. 19, 2008, which claimspriority to JP2007-126948, filed May 11, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improvement of a rear dischargemower of a lawn mower, and a mid-mount type lawn mower that uses therear discharge mower.

2. Description of the Related Art

This type of mid-mount type lawn mower that uses a rear discharge mowerhas, e.g., the following conventionally known structure.

A lawn mower is known in which a power transmission pulley and a powertransmission belt are used as means to transmit power to a plurality ofadjacently positioned blade shafts, in which one of the blade shafts andthe shaft of the power transmission pulley for providing input to theblade shaft are structured as separate shafts in order to drive the twoshafts in mutually reverse directions, and in which a set of gears isprovided to ensure reverse rotation between the two shafts (see JapaneseLaid-Open Patent Application (JP-A) 2003-274728 (Patent Document 1), forexample).

A lawn mower is also known in which a power transmission pulley and apower transmission belt are used as means to transmit power to aplurality of adjacently positioned blade shafts, and in which asupplementary pulley is used to convert the winding direction of thebelt so that the internal peripheral surface side of the powertransmission belt is wound around the power transmission pulley on oneof the blade shafts, and the external peripheral surface side of thepower transmission belt is wound around the power transmission pulley ofanother blade shaft, in order to drive the two shafts in mutuallyreverse directions (see Japanese Laid-Open Patent Application (JP-A)2003-274729 (Patent Document 2), for example).

A lawn mower is further known in which motive power transmitted from aninput shaft is branched at a pair of power transmission shafts toprovide input to a gearbox disposed in the upper portion of left andright blade shafts and to transmit shaft power via a bevel gearmechanism or the like as a means to pivotally transmit power to aplurality of blade shafts in adjacent positions (see Japanese Laid-OpenPatent Application (JP-A) 2003-158907 (Patent Document 3), for example).

In these kinds of rear discharge mowers, the blades are driven at afairly high speed and high torque in order to discharge grass clippingsin a rearward direction by generating airflow and producing a bouncingaction that accompany the rotation of the blades.

If an attempt is made to convey the grass clippings toward the grasscatcher in the rearward and upward directions while minimizing areduction in the movement energy in the grass clippings dischargedirection, it is desirable to gradually change the movement of the grassclippings upward from the conveyance start area in which a conveyanceaction is imparted by the rotation of the blades across to the locationwhere discharge begins on the rearward side where the conveyance actionis completed. In order to accomplish this, it would be advantageous togradually change the movement direction by beginning an upward slope ofthe grass-clippings discharge path from a position as near the front endof the mower deck as possible.

In models having a structure in which motive power is transmitted to theblade shafts using a belt as described in Japanese Laid-Open PatentApplications (JP-A) 2003-274728 and 2003-274729 noted above, the belt isused in a state of high belt tension. Therefore, the strength of theblade shaft support structure and the mower deck must be kept very highbecause the provision of a large distance between the mower deck and thepower transmission pulley results in a situation in which a strongtension operates on the power transmission pulley in a position set at adistance from the mower deck, and there is a possibility that a bendingmoment will forcefully operate on the blade shaft. However, this is notpractical in actual application in a mower deck composed of a thin metalplate because sufficient support strength cannot be obtained and thethickness of the mower deck must be unavoidably increased to assurestrength, and other impractical structural modifications becomenecessary when attempting to set the power transmission pulley at adistance from the mower deck.

For this reason, in the arts described in Japanese Laid-Open PatentApplications (JP-A) 2003-274728 and 2003-274729 noted above, measuresare taken in which the power transmission pulley is not placed at adistance from the mower deck, but rather a supplementary pulley is usedto bring the power transmission belt between adjacent blade shafts tothe front side of the mower deck to the extent possible, and thelocation at which the grass-clippings discharge path portion on themower deck begins an upward movement is set further forward. However,since there is no change in the fact that the power transmission pulleyremains in close proximity on the surface of the mower deck, thelocation at which upward motion starts must be provided further rearwardto avoid [close] placement of the power transmission pulley and belt,and the location at which upward motion starts cannot be broughtsufficiently forward.

Moreover, insofar as a belt is used as the transmission mechanism, somesort of blade reversal mechanism must be used between adjacent bladeshafts, necessitating a dedicated set of gears or a redundantsupplementary pulley for that purpose.

A structure is also conventionally known in which power transmission isbranched by using a pair of power transmission shafts, a bevel gearmechanism, or the like in place of a structure using a belt and powertransmission belt, as described in Japanese Laid-Open Patent Application(JP-A) 2003-158907.

In a structure that drives a bevel gear about the center of a horizontalshaft using a power transmission shaft in this manner, there are nodrawbacks such as the generation of high tension between adjacent bladeshafts, but the following problems arise because placement of a bevelgear with a rather large diameter is difficult on a mower deck that haslittle extra space.

The power transmission mechanism itself, which involves the meshing ofbevel gears with each other, produces a relatively high level of noisein comparison with a power transmission mechanism composed of flatgears. In addition, there is a drawback when the bevel gear itself has asmall diameter in that the noise in the gear meshing portion increasesfurther due to the load that operates in a concentrated fashion on themeshing portion that has a small number of teeth. Also, a separatereverse rotation mechanism naturally becomes necessary.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improvement of thiskind of conventional rear discharge mower.

The rear discharge mower according to the present invention comprisesthe following:

a first shaft;

a first blade that is rotated in unison with the first shaft;

a second shaft that is configured to be rotated in a direction oppositefrom a rotational direction of the first shaft;

a second blade that is rotated in unison with the second shaft, whereina grass-clippings discharge path is formed through which grass clippingsare discharged in a rearward direction from the area between the firstshaft and second shaft as viewed from above;

an enclosing casing that pivotally supports the blade shafts; and

a power train that is accommodated in the enclosing casing and thattransmits power to the first and second blade shafts.

In accordance with the configuration described above, a mower bladedrive casing that supports adjacent blade shafts is provided. Therefore,a configuration is formed so as to have sufficient strength in order tosupport the two blade shafts, whereby the mower deck itself can becomposed of a thin member that has strength in order to shape theintended blade rotation space.

In this embodiment, it is preferred that the enclosing casing have afirst cylindrical shaft casing portion that at least partially enclosesthe first shaft, a second cylindrical shaft casing portion that at leastpartially encloses the second shaft, and a connecting casing portionthat connects the first and second cylindrical shaft casings.

Since the connecting casing portion of the mower blade drive casingconnects together the cylindrical shaft casing portions that support theblade shafts, the connecting casing portion can be disposed in aposition that is set at a sufficient distance from the mower deck bysuitably setting the length of the cylindrical shaft casing portions.Therefore, a starting end of the grass-clippings discharge path can beset nearer to the front end in the direction of the grass clippingsconveyance on the top surface side of the mower deck without beingaffected by the existence of the connecting casing portion, and agrass-clippings discharge path with good grass clipping dischargeperformance can be formed.

In this embodiment, it is preferred that the enclosing casing enclosethe first shaft, the second shaft, and the power train, from a frontside, lateral sides, a rear side, and a top side.

In this embodiment, it is preferred that the power train be configuredwith a plurality of flat gears disposed in the connecting casing portionof the enclosing casing.

In this embodiment, it is preferred that the plurality of flat gears bedisposed in the same plane.

In this embodiment, it is preferred that one of the flat gears bepositioned above the grass-clippings discharge path, and the one flatgear be configured with a smaller diameter than the other flat gears inthe power train.

In this embodiment, it is preferred that one of the flat gears bepositioned above the grass-clippings discharge path, and the position ofthe axial center of rotation of the one flat gear be set to be morefrontward than the axial center of rotation of the other flat gears inthe power train.

In this embodiment, it is preferred that a flat gear to which externalpower is input be disposed in the connecting casing portion, an oddnumber of flat gears be provided to transmit power to the first bladeshaft among the flat gears to which power is transmitted by meshing withthe flat gear to which external power is input, and an even number offlat gears be provided to transmit power to the second blade shaft.

In this embodiment, it is preferred that each of the first and secondblades be disposed so that a rotational trajectory of the first bladeand a rotational trajectory of the second blade overlap each other, andrespective rotational phases be mutually different.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an overall side view of a mid-mount typelawn mower;

FIG. 2 is a diagram showing an overall plan view of a mid-mount typelawn mower;

FIG. 3 is a diagram showing a plan view of a rear discharge mower;

FIG. 4 is a longitudinal sectional view in the lateral direction showinga power transmission system of a rear discharge mower;

FIG. 5 is a transverse sectional view in the horizontal directionshowing the power transmission system of a rear discharge mower;

FIG. 6 is a longitudinal sectional view in the longitudinal directionshowing the power transmission system of a rear discharge mower;

FIG. 7 is a perspective view showing the housing of a rear dischargemower;

FIG. 8 is an explanatory diagram showing another embodiment of thehousing of a rear discharge mower;

FIG. 9 is an explanatory diagram in a plan view showing anotherembodiment of the power transmission system of a rear discharge mower;

FIG. 10 is an explanatory diagram in a plan view showing anotherembodiment of the power transmission system of a rear discharge mower;and

FIG. 11 is an explanatory diagram in a plan view showing anotherembodiment of the power transmission system of a rear discharge mower.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An example of an embodiment of the present invention will be describedbelow in detail with reference to the diagrams. A plurality ofembodiments will be described below. It is to be understood that thecombination of characteristics of one embodiment with thecharacteristics of another embodiment is included within the scope ofthe present invention.

[Configuration of the Lawn Mower]

FIGS. 1 and 2 show a riding-type, mid-mount type lawn mower as anexample of a lawn mower provided with a rear discharge mower accordingto the present invention.

The lawn mower is configured with a mower 2 that is mounted in suspendedfashion so as to be able to be raised and lowered between the frontwheels 11 and the rear wheels 12 of a riding running carriage 1, while agrass catcher 6 is connected so as to be able to be raised and loweredto the rear section of the carriage via parallel four-point linkingmechanisms 13.

An engine 5 is installed in the front of the running carriage 1, powertaken from an output shaft 50 at the front portion of the engine 5 istransmitted via a belt transmission device 51 to an operating powertake-off shaft 52 that is disposed below the front portion of thecarriage, and power from the operating power take-off shaft 52 istransmitted by a shaft to the mower 2.

The rear wheels 12 are configured so that the right and left rear wheels12 are each separately pivotably supported in a cantilevered state atthe lower end of a pair of left and right rear wheel shaft casings 15that protrude facing in the rearward downward direction from both theleft and right sides of a transmission casing 14 that is secured to thecarriage frame 10, and a duct 16 for discharging grass clippings issecured to a space that is formed between the left and right rear wheelshaft casings 15.

The grass catcher 6 is composed of a container main body 60 that isformed in the overall shape of a box and is provided with an entranceopening 61 that faces the running carriage 1 in the grass-catchingposition and is externally fitted and connected to the rear end of theduct 16, and an exit opening 62 that faces the opposite side of theentrance opening. The grass catcher 6 is further composed of a rearportion lid 63 that can open and close the exit opening 62 formed in thecontainer main body 60.

The grass catcher 6, which is connected by a linking mechanism 13 asdescribed above, is configured to be able to change position between agrass-catching position connected to the duct 16 for conveying grassclippings from the running carriage 1 so as to collect grass clippingsthat are conveyed by the power of the airflow from the mower 2, which isinstalled on the running carriage 1, and a discharge position that isset at a distance from the duct 16.

[Mower Configuration]

The mower 2 has a structure in which two rotating blades 21 are arrangedin a row to the left and right within a mower housing 20, as shown inFIGS. 2 and 3, and is formed as a rear discharge mower in which the leftblade 21 is driven in a clockwise direction, and the right blade 21 isdriven in a counterclockwise direction, whereby grass clippings ride ona conveying airflow generated by the rotation of the blades 21 and aredischarged from an exit 20A formed near the rear center portion of themower housing 20. The grass clippings discharged from the exit 20A arebrought to the grass catcher 6 via the duct 16 disposed between the leftand right rear wheels 12.

The mower 2 is configured so that the upper end side is elevatablysuspended and connected to the lower end side of a pair of front andrear swinging links 23 that are pivotally connected to the carriageframe 10, so that the mower will run with gauge wheels 24, which areprovided to the lower end portion of the mower housing 20, in a state ofcontact with the ground when operated to clip grass.

Among the swinging links 23, a portion of the rear swinging link 23 isconnected and interlocked via a connecting rod 26 to a raising andlowering operation lever 25 located to the side of a driver seat 7 thatis provided at the top of the carriage frame 10, and is configured toallow manual raising or lowering operation by swingably operating theraising and lowering operational lever 25.

Blade shafts 22 that support the right and left blades 21 of the mower 2are mutually connected and interlocked via a power train 4 composed of aset of gears that is composed of flat gears 40 housed in a mower bladedrive casing 3, as shown in FIGS. 3 through 5. The mower blade drivecasing 3 is an example of an enclosing casing.

The mower blade drive casing 3 is composed of cylindrical shaft casings30 that enclose the blade shafts 22, and a connecting casing 31 thatconnects the top end sides of the cylindrical shaft casings 30, therebyforming a gate-shaped structure as shown in FIG. 4. The flat gears 40for power transmission are housed in the interior space of theconnecting casing 31.

A gear box 32 is secured to an intermediate portion of the connectingcasing 31. The gear box 32 is provided with a bevel gear 33 that isformed on the end of the power train shaft 53, which is connected to theoperating power take-off shaft 52 on the front side of the carriage, andan input shaft 35 in which a bevel gear 34 that meshes with the bevelgear 33 is provided to the end of the shaft.

A boss section 41 a of an input flat gear 41 fitted over a spline formedon the portion of the power input shaft 35 that projects from the gearbox 32 is supported by a shaft via ball bearings 44 in an intermediatesection of the connecting casing 31, and an odd number of relaying flatgears 43, i.e., a single such gear, is disposed between the input flatgear 41 and the output flat gear 42 fitted over a spline on the shaftends of one of the blade shafts 22. An even number of flat gears 43,i.e., two such gears, are disposed between the input flat gear 41 andthe output flat gear 42 fitted over a spline on the end of the otherblade shaft 22.

The flat gears 40 that constitute the power train 4 are composed of theflat gears 41, 42, and 43. The right and left blades 21 that areconnected and interlocked using the power train 4, which is composed ofthe flat gears 40 in this manner, are disposed so that the rotatingtrack of each blade partially overlaps the other, but the blades aremutually offset in phase in the manner shown in FIG. 3 and assembled sothat collision between the blades 21 is avoided.

Among the flat gears 41, 42, and 43, the flat gears 41 and 42 for inputand output have boss sections 41 a and 42 a that each rest on bearingsinside the connecting casing 31 via ball bearings 44. Also, splines areformed at the input locations and the output locations on the internalperipheral side of the boss sections 41 a and 42 a of the power inputand output flat gears 41 and 42, and the boss sections are configured tobe able to be inserted and removed with respect to the power input shaft35 in which splines are formed and the upper end section of the bladeshaft 22.

The boss sections 41 a, 42 a, and 43 a and the teeth sections 41 b, 42b, and 43 b of the flat gears 41, 42, and 43, are formed to be thick,but the hub portions between these sections are formed to be thin.

A pivot support shaft 45 for the relaying flat gears 43 has a maximumdiameter at the upper end portion, the medial portion of the shaftsupported by bearings has a smaller diameter than the upper end portion,and the lower end side is formed to a smaller diameter smaller than theinternal diameter of the bearing, and is configured to be able to beinserted and removed from above.

The cylindrical shaft casings 30 that house the blade shafts 22 and theconnecting casing 31 are separately formed, but are configured to beintegrally connected by bolts at the connecting flange sections 30A and31A formed at the ends of each casing. The lower ends of the cylindricalshaft casings 30 are formed so that the diameter of the correspondingportions of the cylindrical shaft casings is greater than that of theupper end side; even larger flange parts 30B are formed integrally withthe lower ends; and the assembly is connected by bolts to the mower deck20B.

The mower blade drive casing 3 is thus easy to assemble because themower deck 20B need only be bolted together in a completely assembledstate.

A protruding section 20C that protrudes upward in a gradual fashion fromthe vicinity of the point a in FIG. 3 is formed on deck 20B portion ofthe mower housing 20 in the vicinity of the external peripheral edge ofthe mower deck 20B, as shown in FIGS. 3, 6, and 7. Assuming that animaginary line x that connects the axial centers of the two blade shafts22 together is the start location of grass clippings discharge, theprotruding section 20C forms a gradually upward-sloping surface acrossabout ¾ of the circumference and is configured to smoothly hand offgrass clippings to the duct 16 that trails the exit 20A.

Other Embodiments

Other embodiments of the present invention will be listed next.

[1] In regard to the configuration of the mower blade drive casing 3,the cylindrical shaft casings 30 and the connecting casing 31 may beintegrally formed overall and may be configured using a partially opensection or an opening and closing lid as a structure for removing andinserting the flat gears 40 as well as various shafts and othercomponents of the power train 4, though these possibilities are notdepicted in the diagrams.

[2] In FIG. 8A, the internal height of the mower housing 20 is set to begreater, e.g., about 1.2 times to 1.5 times greater than in the ordinaryconfiguration shown in FIG. 8B. When the height of the mower housing 20is set greater in this manner, the grass clippings can be more finelyshredded because the grass clippings are carried about inside thehousing 20 for a long period of time.

[3] The layout of the flat gears 40 is not limited to a configuration inwhich all the flat gears 40 have substantially the same diameter in themanner of the embodiment described above. For example, the flat gears 40that are positioned above the overlapping location of the rotating trackof the two blades 21 may be configured as flat gears 40 that have asmaller diameter than the flat gears 40 of the blade shaft 22 portion,as shown in FIG. 9.

When the flat gears 40 positioned above the overlapping location of therotating track of the two blades 21 are configured in this manner byusing a flat gear 40 that has a smaller diameter than the flat gears 40of the blade shaft 22 portions, the connecting casing 31 portion of thelocation in which the smaller diameter flat gear 40 is housed can beformed in a shape in which the outside peripheral wall of the casing isbrought inward so as to be moved closer to the small diameter flat gear40 as viewed from above. It then follows that the connecting casing 31is arranged so that the portion that has been brought inward ispositioned above the grass-clippings discharge path in which grassclippings are discharged in a rearward direction through a space betweenthe right and left blade shafts 22. As a result, the rear end of theconnecting casing 31 can be shifted as far forward as possible so thatthe slope start end portion of the grass-clippings discharge path can bebrought as far forward as possible and disposed in the direction inwhich grass clippings are conveyed.

[4] The layout of the flat gears 40 is not limited to one in which theentire configuration is arranged in a single straight line as viewedfrom above, as described above in embodiment [3]. For example, theentire configuration may be arranged along a curved line segment so thatthe flat gears 40 that are positioned forward of the overlappinglocation of the rotating track of both blades 21 are positioned furtherforward than the flat gears 40 of the blade shaft 22 portion, as shownin FIG. 10.

In this case as well, the rear end edge of the connecting casing 31 canbe brought as far forward as possible so that the connecting casing 31,which is disposed so as to be positioned above the grass-clippingsdischarge path in which grass clippings are discharged in a rearwarddirection through a space between the right and left blade shafts 22,can, as a result, be disposed so that the slope start end portion of thegrass-clippings discharge path is brought as far forward as possible inthe grass clippings conveyance direction.

[5] The layout of the flat gears 40 is not limited to one in which theentire configuration is composed of flat gears 40 having substantiallythe same diameter and is arranged in a single straight line as viewedfrom above, as in the embodiment described above. For example, the flatgears 40 that are positioned forward of the overlapping location of therotating track of the two blades 21 may have a smaller diameter than theother flat gears 40, and may be disposed along a curved line segment soas to be positioned further forward than the flat gears 40 of the bladeshaft 22 portions, as shown in FIG. 11.

In this case as well, the rear end edge of the connecting casing 31 canbe shifted as far forward as possible.

[6] The layout of the flat gears 40 is not limited to one in which theentire configuration is disposed in a single plane, as described in theembodiments above, and the set of gears constituting the power train 4may, e.g., be provided in a plurality of upper and lower levels, thoughthis possibility is not depicted in the diagrams.

[7] The power drive 4 disposed in the mower blade drive casing 3 is notlimited to one in which flat gears 40 are used as described in theembodiments above, and power transmission belts and power transmissionshafts may be used.

1. A mower comprising: a mower housing having a mower deck extending ina horizontal direction, the mower deck having a grass cutting roomdefined therein; a first shaft extending in a vertical direction, thefirst shaft having an upper end and a lower end, the lower end of thefirst shaft extending through the mower deck and facing the grasscutting room; a first blade connected to the lower end of the firstshaft and rotated in unison with the first shaft; a second shaftextending in the vertical direction, the second shaft having an upperend and a lower end, the lower end of the second shaft extending throughthe mower deck and facing the grass cutting room; a second bladeconnected to the lower end of the second shaft and rotated in unisonwith the second shaft; a first cylindrical shaft casing substantiallyenclosing the first shaft and pivotally supporting the first shaft, thefirst cylindrical shaft casing including: an upper casing portionenclosing a region of the upper end of the first shaft; a lower casingportion enclosing a region of the lower end of the first shaft; and aflange portion extending radially outwardly from a lower end of aperiphery of the lower casing portion of the first cylindrical shaftcasing, the flange portion of the first cylindrical shaft casing beingfixed to the mower deck; a second cylindrical shaft casing substantiallyenclosing the second shaft and pivotally supporting the second shaft,the second cylindrical shaft casing including: an upper casing portionenclosing a region of the upper end of the second shaft; a lower casingportion enclosing a region of the lower end of the second shaft; and aflange portion extending radially outwardly from a lower end of aperiphery of the lower casing portion of the second cylindrical shaftcasing, the flange portion of the second cylindrical shaft casing beingfixed to the mower deck; a connecting casing interconnecting the uppercasing portion of the first cylindrical shaft casing and the uppercasing portion of the second cylindrical shaft casing; and a power trainenclosed by the connecting casing and transmitting power to the firstshaft and the second shaft, the power train including a first outputgear transmitting the power to the first shaft and a second output geartransmitting the power to the second shaft, the first output gear beingmounted on the first shaft at the upper end of the first shaft, and thesecond output gear being mounted on the second shaft at the upper end ofthe second shaft; wherein the first cylindrical shaft casing has saidupper casing portion enclosing the first output gear, the firstcylindrical shaft casing further including an orifice portion extendingbetween and having a smaller diameter than the upper casing portion andthe lower casing portion of the first cylindrical shaft casing; and thesecond cylindrical shaft casing has said upper casing portion enclosingthe second output gear, the second cylindrical shaft casing furtherincluding an orifice portion extending between and having a smallerdiameter than the upper casing portion and the lower casing portion ofthe second cylindrical shaft casing; and wherein the first cylindricalshaft casing, the connecting casing, and the second cylindrical shaftcasing constitute a gate-shaped structure on the mower deck such that aspace is defined between the connecting casing and the mower deck. 2.The mower as defined in claim 1, wherein each of the first output gearand the second output gear comprises a flat gear; and wherein the powertrain further includes a plurality of flat gears disposed in theconnecting casing and between the first output gear and the secondoutput gear, the plurality of flat gears being disposed in a same planetogether with the first output gear and the second output gear.
 3. Themower as defined in claim 2, further comprising a power-inputting gearbox, the gear box including: a power train shaft connected to a powertake-off shaft; a set of bevel gears; and an input shaft, wherein thepower is inputted from the input shaft to one of the plurality of flatgears.
 4. The mower as defined in claim 2, further comprising: aplurality of pairs of upper/lower holes defined on the connectingcasing, the holes including upper holes defined on a top wall of theconnecting casing and lower holes defined on a bottom wall of theconnecting casing to be aligned with the respective upper holes; and aplurality of pivot support shafts removably inserted through therespective upper/lower holes to be attached to the connecting casing,the respective flat gears being journaled on the pivot support shafts.5. The mower as defined in claim 4, wherein each of the upper holes hasa diameter thereof different from a diameter of each of the lower holesaligned therewith; and each of the pivot support shafts comprises astepped shaft having a first stepped portion having a diameter thereofcorresponding to the diameter of its associated upper hole, and a secondstepped portion having a diameter thereof corresponding to the diameterof its associated lower hole.
 6. The mower as defined in claim 5,wherein the diameter of each of the upper holes is larger than thediameter of each of the lower holes aligned therewith; and the pivotsupport shafts are removably inserted from through the respective upperholes.
 7. The mower as defined in claim 6, wherein each of the pivotsupport shafts has an upper end shank portion, an intermediate shankportion and a lower end shank portion, a diameter of the upper end shankportion being larger than a diameter of the intermediate shank portion,and the diameter of the intermediate shank portion being larger than adiameter of the lower end shank portion; and the upper end shank portionis fitted in the upper hole associated therewith and the lower end shankportion is fitted in the lower hole associated therewith.
 8. The moweras defined in claim 1, further comprising a protruding section protrudedfrom the mower deck, the protruding section being accommodated in thespace.
 9. The mower as defined in claim 8, further comprising apower-inputting gear box, the gear box including: a power train shaftconnected to a power take-off shaft; a set of bevel gears; and an inputshaft; wherein the power is inputted from the input shaft to one of theplurality of flat gears.
 10. The mower as defined in claim 8, wherein awherein a rotational trajectory of the first blade and a rotationaltrajectory of the second blade overlap with each other, and a rotationalphase of the first blade and a rotational phase of the second blade aredifferent from each other.
 11. A mid-mount type lawn mower tractor,comprising the mower according to claim 8 disposed between front andrear wheels of the tractor.